Design and characterization of advanced battery technologies and mechanistic studies of the oxygen reduction reaction for fuel cells

Abstract

About one fifth of the world’s energy consumption comes from the transportation sector. To fully address the problems associated with climate change, pollution, and energy security, the transportation sector must transition away from fossil fuel-based energy sources. When coupled with clean and renewable energy production technologies such as solar and wind, vehicles powered by batteries or hydrogen fuel cells could enable this transition. Automobiles powered by Li-ion batteries have already been commercialized on a modest scale, but these vehicles suffer from limited range, temperature intolerance, and high production costs. The performance of Li-ion batteries must substantially improve to facilitate the widespread implementation of electric vehicles. Alternatively, altogether new battery chemistries that promise higher energy densities can be employed. Chapters 2-6 of this thesis investigate two battery chemistries, the Li-O2 and Mg-ion batteries, which have higher theoretical energy densities than current Li-ion batteries. Results from a wide variety of analytical techniques underscore some of the largest hurdles hindering the commercialization of these devices. Several examples of new materials and operating procedures suggest potential directions to pursue to overcome these problems in the future. The last three chapters of this thesis investigate fundamental questions that relate to hydrogen fuel cells. The sluggish nature of the O2 reduction reaction to water, which occurs at fuel cell cathodes, is one of the main obstacles preventing the widespread commercialization of these devices. Despite many decades of research, precise mechanistic understanding of this important reaction remains elusive, thereby obfuscating rational catalyst design. This work describes the development of a unique electrochemical platform called a hybrid bilayer membrane that enables the kinetics of proton transfer to an O2 reduction catalyst to be controlled. The insight gained from this novel approach highlights the subtle interplay between proton transfer, electron transfer and bond-breaking events that occurs during O2 reduction, which should aid future catalyst development